NTSB Factual Report

HISTORY OF FLIGHT

On April 24, 2016, at 1706 Pacific daylight time, a DG Flugzeugbau GmbH DG-800B, N800YG, struck trees during landing near Clements, California. The motorglider was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot was not injured, and the glider sustained substantial damage. The cross-country personal flight departed Byron Airport, Byron, California, at 1417. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot utilized a tow-plane for departure. About 2 1/2 hours into the flight, while on the return leg to Byron, the glider encountered reduced lift conditions, and descended to about 2,400 ft above ground level (agl). Unable to maintain altitude, the pilot selected a field for landing about 5 miles away. His intention was to perform an engine air-start prior to touchdown, and then return to Byron under powered flight. Should the engine not start, he would proceed with the landing.

The pilot overflew the field while descending from 1,700 to 1,100 ft agl, and during the downwind leg, he configured the glider for landing, and extended the retractable propeller mast. He could not get the engine to start, but reported that this was not unusual for a first start attempt, so he made two more attempts. However, each time the engine would rotate and "cough" as the starter was engaged, but not continue under its own power.

Having now descended to 500 ft agl, and without enough time to retract the propeller mast, he initiated the base turn for landing. During the turn, he realized that the wind conditions were stronger than anticipated, and he would not be able to reach the landing spot. Without a safe alternate landing site, he continued the approach, landing short and into a group of eucalyptus trees.

The glider came to rest left wing down, with the cabin resting about 10 ft in the air against a tree trunk. The pilot was able to secure the glider, open the canopy, and climb to the ground. The left wing fragmented during the accident sequence, and the tailboom twisted away from the main cabin along the longitudinal axis.

GLIDER INFORMATION

The composite glider was manufactured by DG-Flugzeugbau GmbH in Germany in 1998, and exported to the United States that year. At the time of the accident, it was registered in the experimental/exhibition category. It was equipped with a 53 horsepower SOLO 2625-01 two-stroke engine, and a two-blade composite propeller.

The engine and propeller were attached to an electrically-driven pivoting mast assembly located behind the cabin. The assembly was stowed in the upper fuselage, and could be extended and retracted automatically at engine start or manually using cockpit controls.

The most recent condition inspection was completed on April 3, 2016. At that time, the airframe had accumulated a total time of 2,062.7 flight hours, with an engine total time of 98.5 hours. Maintenance logbooks indicated that at the time of the prior inspection in July 2014, the airframe total time was 2,048.6, and engine time was 97.6 hours.

The pilot reported that the engine was last operated on October 17, 2015, as an in-flight start. In November of that year, he "winterized" the engine in accordance with the engine's operation manual, by injecting two-stroke oil into the carburetor, cranking the engine ten turns by hand, and then covering the carburetor intake and the exhaust muffler outlet. The manual recommended that for any period of inactivity greater than 60 days, the fuel tank should be drained. The pilot reported that he did not drain the tank in November, but instead topped it off with a 50:1 premix of 100 low-lead aviation fuel and two-stroke oil.

The engine was not started during the annual inspection, 21 days prior to the accident, but during the inspection the pilot did rotate the engine by hand, confirming smooth operation.

TESTS AND RESEARCH

The airframe and engine were examined by the NTSB investigator-in-charge following recovery from the accident site. The examination did not reveal any mechanical malfunctions or failures that would have precluded normal operation. The fuel tank contained 6 liters of fuel (22 liters maximum, 0.5 liters unusable). The engine and propeller mast assembly was extended in accordance with the flight manual instructions, and the engine started on the third attempt. Multiple subsequent engine starts and runs were performed successfully, and the engine was operated at varying speeds.

ADDITIONAL INFORMATION

The warnings section of the gliders flight manual made the following recommendation,

"With a motorglider never rely completely on the engine extending and starting. Plan your flight path so that you are always able to carry out a safe outlanding if necessary. Be aware that with the engine extended but not running the rate of sink increases remarkably. This means that with a motorglider you have to decide earlier for an outlanding than with a pure sailplane."

Furthermore, the normal procedures section stated the following,

"With the engine extended but not running the rate of sink at 49 kts increases to 395 ft/min. Therefore restarting the engine should only be done over landable terrain and not below 1,320 ft above ground. But it is better to restart the engine at 660 ft over a landable field rather than at 1,320 ft over a forest or unlandable scrub. Should a flight be conducted over a wide expanse of unlandable terrain, the engine should then be restarted at 3,300 ft above ground level so that if the engine does not start, all the emergency starting procedures can be followed in peace including retraction of the engine if necessary."

The pilot reported no mechanical malfunctions or failures with the glider and engine, noting that in his experience self-launching gliders are prone to starting difficulties, especially after a period of non-use, and that he should not have relied upon the engine to prevent an outlanding.

The pilot acknowledged that the accident was the result of a series of events including: a lack of flight currency on his part, (his last flight occurred in October 2015); his decision to start the flight late in the day and attempt a return in deteriorating conditions; his failure to initiate the engine restart at a higher altitude, along with his omission to run the engine prior to the accident flight after an extended period of non-use and spending too much time and attention on engine start and not enough on landing.

NTSB Probable Cause

The motorglider pilot's decision to perform an in-flight engine start with insufficient altitude, which resulted in an off-airport landing and collision with trees after the engine did not start. Contributing to the accident was the pilot's distraction by the engine restart procedures during a critical portion of the landing approach.